The present invention relates to a particle having a molar ratio of ZnO/Sb.sub.2 O.sub.5 in a range of from 0.8 to 1.2, having a crystal structure of zinc antimonate anhydride (ZnSb.sub.2 O.sub.6) and a primary particle size in the range of from 5 to 500 nm, and to a sol of these particles and a method for producing these particles and sol. The particle of the present invention is used in a variety of applications such as flame retardants for plastics, smoke suppressants, antistatic agents for plastics and glass, and resistors.
Acta Chemica Scandinavia, A, Vol. 29, pp. 803-809 (1975) discloses a zinc antimonate (ZnSb.sub.2 O.sub.6) prepared by heating zinc oxide and diantimony trioxide to 800.degree. C. at a time scale of 4 hours to 3 weeks, by pulverizing the heated mixture, annealing the pulverized mixture at a temperature ranging from 900 to 1,000.degree. C. at a time scale of 4 hours to 2 weeks, and gradually cooling the annealed mixture to room temperature. Zeitschrift fuer Kristallographie, Vol. 98, pp. 185-190 1937 presents observation data of X-ray diffraction of zinc antimonate anhydride {Zn(SbO.sub.3).sub.2 }. American Mineralogist, Vol. 40, pp 64-69 (1955), and Geological Society of America Memoir, Vol. 85, pp. 209 (1962) present observation data of X-ray diffraction of zinc antimonate anhydride (ZnSb.sub.2 O.sub.6, Ordonezite).
JP-A-3-267143 (the term "JP-A-" referred to hereinafter signifies "unexamined Japanese patent publication") discloses a composition consisting of zinc oxide and diantimony pentoxide which was prepared by mixing an acidic aqueous sol of diantimony pentoxide and basic zinc carbonate at a molar ratio of ZnO/Sb.sub.2 O.sub.5 in a range of from 0.5 to 10 to form a uniformly dispersed slurry, performing decarbonation of the basic zinc carbonate in the slurry at a temperature range of from 50 to 100.degree. C. to a molar ratio of CO.sub.3 /ZnO in a range of from 1/5 to 1/500, and by drying the slurry in a temperature range of from 150 to 250.degree. C.
The method disclosed in Acta Chemica Scandinavia described above produces zinc antimonate anhydride by mixing zinc oxide and diantimony trioxide and by calcining the mixture. The particle size of the obtained zinc antimonate anhydride is, however, not given in the description. Since ordinary diantimony trioxide has a large primary particle size, the primary particle size of zinc antimonate anhydride obtained by this method is 500 nm or more. Accordingly, when particles of this type are used as a flame retardant or smoke suppressant, they do not provide a completely satisfactory effect. In addition, particles of this type have the disadvantage of not providing a sol even by pulverizing, because of their large primary particle size. The method disclosed in JP-A-3-267143 employs a low calcining temperature so that the product has a primary particle size of 500 nm or less. Nevertheless, X-ray diffraction measurement shows a peak of diantimony pentoxide and not a peak of zinc antimonate anhydride. Consequently, the product thereof is not zinc antimonate anhydride.
The present invention provides a particle having a molar ratio of ZnO/Sb.sub.2 O.sub.5 in a range of from 0.8 to 1.2, a crystal structure of zinc antimonate anhydride (ZnSb.sub.2 O.sub.6) and a primary particle size in the range of from 5 to 500 nm, relates to a sol of these particles and a method for producing these particles and their sol.